Given the geographically, culturally, and chronologically widespread occurrence of mystical experience and the important place it has held in the creation of cultures and civilizations, mystical experience is not something that can be ignored or cast aside as unnecessary or insignificant. On the contrary, the evidence indicates that mystical experience is an innately and universally human phenomenon that has played a significant role in the shaping of historical events. That it is innate and universal does not imply that all persons will have such experiences. Rather, what is meant by innate and universal is that these experiences have occurred to a number of individuals in nearly every culture in the world and these individuals have in large part claimed that these experiences are possible for others given the right conditions and effort toward that end. Mysticism, then, stands in need of an explanation if one is to hold a worldview that is consistent with the facts of actual human experience. There are three possible explanations, though not each is equally plausible.

One possible explanation of mystical experiences, and perhaps the first resort of the strict materialist who wishes to maintain his worldview intact, is that those who claimed to have undergone such experiences are, simply put, lying. It is possible for the atheist to argue that many of these experiences exist only within the realm of legend and hearsay. The experience of the Buddha, for example, was not written down for some years after his lifetime and may reflect legendary accretions to his original account of whatever happened to him under the bodhi tree. It may very well be the case the bodhi tree itself is such a legendary accretion. The biblical accounts of the experiences of Abraham, Moses, and the apostles have been the subject of particularly vehement attacks by modern atheists, given the Western cultural context in which most atheists have been bred. Those cases that fall within the more potentially trustworthy record of history, such as the claimed experiences of Benedict of Nursia, Muhammad, Thomas Aquinas, Guru Nanak, and Blaise Pascal, cannot be dismissed so easily as legendary accretion. If one is to hold that all accounts of mystical experience are fabrications these cases must be deemed cases of intentional fabrication.

The motivation for such a fabrication on the part of many of these figures seems wanting, however. While one might argue that Muhammad, for example, created a story of a vision of an angel and his subsequent revelations from God in order to unite the disparate Arab tribes and forge the new political and military power he did indeed create, others among those who made the claim of a mystical experience seem to have had no such ulterior motive. In Aquinas’s case, the mystical vision he claimed to have experienced led him to abandon his writing, the very act through which he gained fame and honor. Pascal kept his mystical experience a secret throughout his life and never attempted to gain wealth, prestige, or any other goods from it.

There is, in addition, the problem of the widespread nature of these claims. These claims have occurred, as has been shown, in a wide variety of locations and are spread out through the whole of recorded history and beyond. In addition, as has been shown through the use of William James’s four criteria of authentic mystical experience, the reported mystical experiences bear a great deal of similarity to each other, an especially surprising fact given the wide divergence in cultural context and idiom between the various claimants to these experiences. For the position that each of these claims are intentional fabrications to be a claim that accurately accounts for all cases, it must be maintained that multiple individuals independently invented nearly identical fabrications. If this were the truth, it would be more miraculous than if the mystical experiences themselves are true!

A second possible explanation for the occurrence of mystical experiences is that the experiences have their source not in contact with a divine and transcendent being but rather as the product of physical processes. It may be that these experiences were hallucinations of one sort or another. One proposed physical explanation that has maintain its popularity since it was first posited is the idea that these mystical experiences may be the product of epileptic seizures. The response of the early 20th century occultist Aleister Crowley to just this assertion regarding claims of mystical experience seems as appropriate today as when he wrote it over a hundred years ago, however: “Even if epilepsy were the cause of these great movements which have caused civilization after civilization to arise from barbarism, it would merely form an argument for cultivating epilepsy.”

Mystical experiences have been the defining moments in the lives of those who have had them. Aquinas stopped writing; Pascal began writing; Paul became the leading advocate for the religion he would eventually die for. Mystical experiences have been the defining and originative moment in nearly all of the world’s great civilizations. The culture of East Asia is in large part the product of the Buddha’s experience under the bodhi tree. Western Civilization is the product of the conglomeration of the movements that resulted from the experiences of Abraham and Moses, the prompting of Socrates’s daemon, and the visions of James, John, Peter, and Paul. Islamic civilization traces its origins to Muhammad’s vision of Gabriel in a cave in Arabia. That the great bulk of mankind lives within a civilization that is the product of a mystical experience and that the greatest achievements of mankind have been the products of these civilizations seems a fine case for cultivating epilepsy or whatever other mental illness is responsible for these visions in the first place, if indeed they are the product of mental illness. Indeed, it seems rather to be the case that the common state of rational thought and ordinary brain functioning is the worse of the two possibilities and is itself the illness if hallucinatory man creates civilizations while rational man merely lives within them and enjoys the benefits of the insanity of the former.

There is a third explanation, however, and this is the most plausible of the three, when the implications of the former two proposed explanations are taken into account. The third possible explanation for mystical experience is that these experiences are, in all truth, authentic experiences of a divine and transcendent order or being. The implications of such an explanation of mystical experience are, no doubt, quite extensive. If mystical experiences are authentic, God does exist and religion, at least one of them, is correct.

Religion is at the core of nearly all of the world’s civilizations. It hardly needs to be argued, for example, that Indian culture, in its food, dress, custom, and other features, is in large part a derivative of the Hindu belief system. Buddhism, Confucianism, and Taoism are quite obviously the formative elements underlying Chinese and Korean culture. The synthesis of Judaism and Hellenism within the context of Christianity is quite obviously at the heart of Western Civilization. The modern Middle East would be altogether different were it not for the cultural predominance of Islam in that region. In turn, the root and stem of each of these various religious systems is an experience like that described by William James. Nearly all of the world’s major religions have as their source a claim by their founder to have directly experienced something divine and transcendent, to have attained a suprarational awareness. In short, a claim of mystical experience is at the beginning and center of each of the world’s cultures. It is these experiences that will now be turned to as evidence that mystical experience is a widespread and innately human phenomenon that must be accounted for in any coherent belief system that remains true to reality.

The experience of the Buddha is the source of the central doctrines and practices of Buddhism, one of the most popular religious systems in the world and one that has had a major formative influence on nearly all of East Asia. While there are no firsthand accounts by the Buddha concerning his experience, early Buddhist documents like those contained in the Sutta Pitaka, a collection of sutras the contents of which have traditionally been attributed to the Buddha and his closest disciples, provide insight into the nature of the Buddha’s experience.

The descriptions of this experience meet all four criteria employed by William James to describe mystical experiences. The Buddha’s employment of the ambiguous term “nibbana,” meaning “extinguishing,” to describe his experience indicates the ineffable nature of the experience. Throughout the important Buddhist texts, nibbana is consistently described in terminology that is often obscure and almost always phrased in the negative, indicating what it is not rather than what it is. The Nibbana Sutta, for example, records that the Buddha claimed,

There is that dimension where there is neither earth, nor water, nor fire, nor wind; neither dimension of the infinitude of space, nor dimension of the infinitude of consciousness, nor dimension of nothingness, nor dimension of neither perception nor non-perception; neither this world, nor the next world, nor sun, nor moon. And there, I say, there is neither coming, nor going, nor stasis; neither passing away nor arising: without stance, without foundation, without support. This, just this, is the end of suffering.

Similarly, the second century AD Buddhist philosopher Nagarjuna wrote that, “The [Buddha] has declared that earth, water, fire, and wind, long, short, fine and coarse, good, and so on are extinguished in consciousness. … Here long and short, fine and coarse, good and bad, here name and form all stop.”

The enlightenment experience of the Buddha also possessed the noetic quality of a sudden flash of insight or illumination. The Mahasuccaka Sutta features a dialogue that claims to record the words of the Buddha himself. In the course of the dialogue, the Buddha reports that as he grew closer to enlightenment multiple insights “spontaneous, never before heard” became apparent to his mind. These insights finally culminated in a vision like the cosmic vision reported by Benedict and Arjuna. The Buddha says that he saw all at once “many eons of cosmic contraction, many eons of cosmic expansion, many eons of cosmic contraction and expansion.” The Four Noble Truths and the Eightfold Path, the teachings of the Buddha which form the core of Buddhist belief and practice, were then revealed to him as flashes of insight. The Buddha concludes, “Ignorance was destroyed; knowledge arose; darkness was destroyed; light arose.”

The Buddha concludes his description of his experience with an indication of its transient quality: “But the pleasant feeling that arose in this way did not invade my mind or remain.” The language used throughout the description, in which the Buddha indicates his passive reception of the insights and experience, demonstrate also the fourth of James’s criteria, passivity.

The far different cultural context of the Ancient Near East was the home of men whose similar experiences gave birth to a quite different system of religious thought. The first two books of the Bible record the experiences of the two founding figures of Judaism, Abraham and his descendent Moses, each of whose experiences bear the same qualities delineated by James.

While Genesis records several interactions of Abraham with God, God’s appearance to Abraham in the form of three travellers is particularly exemplary in its exhibition of all four characteristics typical of mystical experience. The three visitors arrive suddenly and unexpectedly. Genesis 18:1-2 reports that “the Lord appeared to him by the oaks of Mamre, as he sat at the door of his tent in the heat of the day. He lifted up his eyes and looked, and behold, three men were standing in front of him. When he saw them, he ran from the tent door to meet them and bowed himself to the earth.” As in the case of the Buddha, a profound insight is granted. Unlike the Buddha, the insight does not arrive in the form of a cosmic vision or a sudden flash of doctrinal truth. Rather, the insight granted is that Abraham’s wife Sarah will conceive and bear a son, Isaac, through whom Abraham will become the father of a great nation of people dedicated to the worship of the one true God, an insight the ramifications of which continue to be exhibited today in the adherence of half of the world’s population to a religious tradition which traces the origins of its most basic beliefs to Abraham.

The Book of Exodus records the experiences of Moses, a descendant of Abraham and, in a sense, the foundational figure of Judaism, as the prophet through whom the law was given to the Jewish people. Two incidents in the life of Moses are especially exemplary of the nature of mystical experience, the incident at the Burning Bush and the giving of the commandments on Mount Sinai. Exodus 3 reports the former incident as an entirely unexpected and profoundly life-altering event. As Moses was tending the sheep of his father-in-law, says the Exodus 3:2, “He looked, and behold, [a] bush was burning, yet it was not consumed.” As Moses approached to investigate this strange phenomenon, a voice suddenly called his name from the bush, ordering him to remove his sandals out of reverence for the holiness of the ground on which he stood. With Moses prostrate on the ground before the bush, God then provided the unexpected insight that Moses was to act as a prophet to free his people from slavery in Egypt. The ineffable quality of this already stunning event is further exhibited in God’s self-description of “I am that I am” (Exodus 4:18), a profound phrase that continues to be the subject of controversy and contemplation in the several religious traditions that claim the story of Moses as part of their spiritual lineage. The Christian mystic Gregory of Nyssa, commenting on this passage in his Life of Moses, summarizes the profound insight granted to Moses:

It seems to me that what the great Moses learned in the theophany is simply this, that neither those things grasped by sense, nor those that the mind can understand, have a real existence. The only reality that truly exists is the one that is above all of them, the cause of all from which everything depends.

The later self-revelation of God to Moses on Mount Sinai also exhibits the qualities described by William James. Moses is called by God in Exodus 19:20 to ascend Mount Sinai and there to meet with him. It is on the mountain that God reveals the law for the Jewish people to Moses. That Moses must meet with God in a cloud on the mountain is indicative of the ineffability of the experience, as is the later revelation, in Exodus 33:23, of God’s back to Moses, whereas God refuses to reveal his face to him.

The experience of the apostles Peter, James, and John on Mount Tabor as recorded in Matthew 17 follows the experience of Moses on Mount Sinai as its model and again exhibits the qualities described by William James. Matthew 17:1 reports that Jesus selected these three apostles and “led them up on a high mountain by themselves.” There, “he was transfigured before them, and his face shown like the sun, and his clothes became white as light” (Matthew 17:2). The passivity of the three apostles is indicated in their being led and being shown; rather than acting as active agents in the experience it is something that is revealed to them by a power much greater than all of them.

Peter’s bewildered and bewildering reaction to the vision is indicative of the ineffability of the experience. While James and John remain altogether silent, Peter bizarrely offers to build tents for Jesus as well as Moses and Elijah, who have appeared alongside him. While commentators have noted, in the way of an explanation for Peter’s strange offer, that it is tradition to build and dwell in tents on the Jewish Feast of Tabernacles, the offer, made at that moment, has a ring of the absurd and can only ultimately be explained by Peter having been so overwhelmed at the vision he was witnessing as to lose the power of coherent, rational thought and speech. Before Peter can finish his sentence, the voice of the Father spoke from a cloud that surrounded them, granting the flash of insight, “This is my beloved son, with whom I am well-pleased; listen to him” (Matthew 17:5). Finally, with the apostles unable to bear it any longer, the vision ends, as Jesus tells them to rise, “and when they lifted up their eyes, they saw no one but Jesus only” (Matthew 17:8).

The famous appearance of Jesus to Paul on the road to Damascus also exhibits the qualities described James. As Acts 9:3 records, “as he went on his way, he approached Damascus, and suddenly a light from heaven shone around him.” This unexpected light stupefies Paul and knocks him to the ground. He is then granted the profound insight that the very Jesus whose followers he was persecuting is his God. Stunned by this experience and the insight it gave him, Paul remained blind and refused to eat or drink for three days after the experience, says Acts 9:9. Paul, of course, later became the most prolific and well-travelled of the apostles, writing the majority of the books that now comprise the New Testament and travelling nearly the entirety of the eastern Mediterranean in search of converts to Christianity.

As a religious tradition, Christianity in particular has continued to emphasize and focus upon mystical experience as the culmination of religious life toward which all should aim. In the fourth century, the influential Christian bishop Basil of Caesarea described the kinds of experiences reported by those adherents of the then-burgeoning monastic movement in Syria and Egypt, exhibiting once again the criteria delineated by William James:

Utterly inexpressible and indescribable is Divine beauty blazing like lightning; neither word can express nor ear receive it. If we name the brightness of dawn, or the clearness of moonlight, or the brilliance of sunshine, none of it is worthy to be compared with the glory of true light, and is farther removed therefrom than the deepest night and the most terrible darkness from the clear light of midday. When this beauty, invisible to physical eyes and accessible only to soul and thought, illumined some saint, wounding him with unbearable yearning desire, then, disgusted by earthly life, he cried: “Woe is me, that I sojourn in Mesech, that I dwell in the tents of Kedar!” … “My soul thirsteth for God, for the living God.” … Oppressed by this life, as by a prison, how irresistible was the striving towards God of those whose soul was touched by Divine yearning. Owing to their insatiable desire to contemplate Divine beauty, they prayed that the sight of God’s beauty should last for all eternity.

Such experiences, within the Christian tradition, are not confined to the fourth century. On the contrary, there is not an era within the entire history of the Christian Church that has not had its great mystics, including the modern era. Within recent history are mystics like the 19th century Russian monk Seraphim of Sarov, about whom a number of witnesses have recorded their own accounts. Seraphim himself related that one particularly striking experience came upon him unexpectedly while, like Thomas Aquinas centuries before him, he was performing the Eucharistic liturgy. Standing at the altar, he later reported, he suddenly saw an overwhelmingly bright white light, into which appeared Jesus surrounded by a multitude of angels “as by a swarm of bees.” The vision appeared to him only briefly, as in a flash, but so struck him that he was unable to continue with the liturgy. He had to be carried away from the altar to a place where he stood for nearly two hours until he could “come to his senses.”

While the origins of the Judeo-Christian roots of Western Civilization are evident in the mystical experiences of prophets like Abraham and Moses and apostles like Peter and Paul, the mystical experiences which comprise the origins of the Greek roots of Western Civilization are often overlooked. While Plato offers no description of the mystical experiences of Socrates, he does indicate clearly in the Apology that Socrates, that founding figure of the Greek philosophical tradition, believed himself to be prompted to his philosophical inquiry by a divine entity. In the Apology, Socrates explicitly claims to have had “visions,” saying, “And this is a duty which the God has imposed upon me, as I am assured by oracles, visions, and in every sort of way in which the will of divine power was ever signified to anyone.” Elsewhere in the Apology, Socrates explains, “You have often heard me speak of an oracle or sign which comes to me … This sign I have had ever since I was a child. The sign is a voice which comes to me and always forbids me to do something which I am going to do, but never commands me to do anything.” While Socrates does not expand upon or describe these experiences, his words are indicative of mystical experiences. Like the Buddhist civilization of the East, then, Western Civilization has, at its roots, both Hellenic and Hebrew, in mystical experience.

At what might, without inaccuracy, be termed the outer boundaries of Western Civilization mystical experience took a quite similar shape and these experiences, in turn, gave birth to the unique and formidable civilizational bloc of Islam. On the Arabian peninsula in the seventh century a merchant named Muhammad reported that he had been the recipient of a number of mystical visions, the first of which took place while he meditated in a cave near the city of Mecca. According to Muhammad, an angel appeared to him in the cave and greeted him with an exclamation that permanently altered Muhammad’s own life as well as the course of all subsequent history:

Recite in the name of your Lord, Who has created all that exists. He has created humankind from a clot. Recite! And your Lord is the most generous Who has taught mankind by the pen. He taught humankind what he knew not.

Muhammad continued to receive these visions until his death, more than 20 years later. The early Islamic scholar Jami at-Tirmidhi recorded that, when asked by one of his followers what it was like when the revelations came to him, Muhammad described them by saying that

Sometimes it comes to me like the ringing of a bell and that is the hardest upon me, and sometimes the angel will appear to me like a man, and he will speak to me such that I understand what he says.

Jami also reports that Aisha, one of the wives of Muhammad, claimed to have observed him “while the Revelation was descending upon him on an extremely cold day.” When “it ceased,” says Aisha, “his forehead was flooded with sweat.”

As in the cases already examined, the visions and revelations experienced by Muhammad also meet the criteria elucidated by William James. According to the descriptions provided by Muhammad and Aisha of his state during the revelations, they seem to have come upon him suddenly and with great force, aspects of the experiences which evince the quality of passivity as described by James. Muhammad’s experiences also demonstrate the noetic quality James identified in that each experience was followed by his recital of certain poetic verses, later compiled to form the Qur’an, which had ostensibly been revealed to him by an angel. In addition, Muhammad’s revelations exhibit the criteria of transiency in their relatively limited duration. Muhammad’s experiences were not a sustained state but a frequent and unexpected break from his normal state of mind and conduct. Muhammad’s visions also bear the quality of ineffability. Those descriptions of his visions which Muhammad was able to provide bear a dreamlike quality which often characterizes descriptions of the ineffable. In his account of one famous vision in which Muhammad claimed to have journey through the heavens the early Islamic commentator Sahih Bukhari records that Muhammad described the vision beginning while he was “in a state midway between sleep and wakefulness.” When “an angel recognized me as the man lying between two men,” he says,

A golden tray full of wisdom and belief was brought to me and my body was cut open from the throat to the lower part of the abdomen and then my abdomen was washed with Zam-zam water and my heart was filled with wisdom and belief.

This dreamlike quality features in a number of descriptions of mystical experiences from various cultural contexts. A vision described by the Native American mystic Black Elk, for example, is similarly dreamlike. He describes being taken into the heavens by a horse that was able to speak and, once in the heavens, watching a variety of horses dance around him:

And when he whinnied to the east, there too the sky was filled with glowing clouds of manes and tails of horses, in all colors singing back. Then to the south he called, and it was crowded with many colored, happy horses, nickering.

Then the bay horse spoke to me again and said: “See how your horses all come dancing!” I looked, and there were horses, horses everywhere — a whole skyful of horses dancing round me.

“Make haste!” the bay horse said; and we walked together side by side, while the blacks, the whites, the sorrels, and the buckskins followed, marching four by four.

The dreamlike mystical experience of Guru Nanak Dev Ji in India near the end of the 15th century led him to found Sikhism, which is today the fifth largest religion in the world. According to early Sikh traditions recorded in the Janamakshi, a biography of Nanak, and other writings, Nanak was accustomed to bathing in and praying beside a river nearby his home early in the morning. On one such journey, Nanak disappeared for the duration of three days during which, he later reported, he stood as if in a trance in the presence of God. Even after reappearing, Nanak did not speak for several days and behaved strangely, having been deeply affected by his strange experience. When he did speak, finally, he proclaimed that God had revealed to him that “there is no Hindu and no Muslim.” In a radical departure from the notions that were current in his cultural context, Nanak spent the remainder of his life preaching a radical vision of absolute human equality before God that encompassed those of all religions, sexes, and races. Nanak later composed a number of poems and songs that reflect the tremendous and overwhelming power of the presence he had experienced during his vision, such as this from the Guru Granth Sahib, a massive compilation of all of the Sikh scriptures:

Were I to live for millions of years and drink the air for my nourishment;

Were I to dwell in a cave where I beheld, not sun or moon, and could not even dream of sleeping,

I should still not be able to express Thy worth; how great shall I call Thy name?

O true Formless One, Thou art in Thine own place —

As I have often heard I tell my tale — If it please Thee, show Thy favour unto me.

Were I to be felled and cut in pieces, were I to be ground in a mill;

Were I to be burned in a fire, and blended with its ashes,

I should still not be able to express Thy worth; how great shall I call Thy name?

Were I to become a bird and fly to a hundred heavens;

Were I to vanish from human gaze and neither eat nor drink,

I should still not be able to express Thy worth; how great shall I call Thy name?

Nanak, had I hundreds of thousands of tons of paper and a desire to write on it all after the deepest research;

Were ink never to fail me, and could I move my pen like the wind,

I should still not be able to express Thy worth; how great shall I call Thy name?

There are significant differences between the doctrines of the world’s various religions. These differences should not be ignored or minimized. They will, however, be temporarily set aside here as the focus will be upon the widespread nature of mystical experience rather than upon the divergent aspects of these experiences as they have been reported by adherents to various systems. While the experience of a Hindu mystic in Upanishadic India is undoubtedly different in important ways from that of a Christian mystic in the Egyptian desert of the 5th century, there are definite shared features in the descriptions of each experience which indicate the experiences to be of a similar, even if not identical, nature. It is these similar features which will be focused upon for the purposes of this paper.

In his survey of accounts of mystical experiences, psychologist William James discerned four characteristics shared by all of these experiences. These four characteristics described by James in his Varieties of Religious Experience provide an outline of the criteria by which an experienced can be determined to fit within the category of mystical experience. These four marks are:

1. Ineffability. The experience is indescribable, or nearly so. Words are insufficient to the task of accurately expressing the contents of the experience. This is demonstrated, for example, in the previously discussed experiences of Aquinas and Pascal, and in their mutual inability to articulate their experience without resorting to poetic imprecision.

2. Noetic quality. The experience provides a profound insight into the nature of reality that could not, apparently, be reached through the rational faculties on their own. The sixth century bishop of Rome and Christian mystic Gregory the Great describes, for example, an experience of Benedict of Nursia, the famous founder of European monasticism, in which he described seeing “the whole world … brought before his eyes, gathered together, as it were, in one ray of light.” Benedict’s experience, as described by Gregory, bears a great deal of resemblance to the more ecstatic and extended vision of Arjuna recorded in the Hindu spiritual classic The Bhagavad Gita. There, when God reveals himself to Arjuna, Arjuna is “filled with wonder and his hairs stand on end.” He exclaims,

O Lord of the universe, I see You everywhere with infinite form, with many arms, stomachs, faces, and eyes. Neither do I see the beginning nor the middle nor the end of Your Universal Form.

…

I see You with infinite power, without beginning, middle, or end; with many arms, with the sun and the moon as Your eyes, with Your mouth as a blazing fire whose radiance is scorching all the universe.

The entire space between heaven and earth is pervaded by You alone in all directions. Seeing Your marvelous and terrible form, the three worlds are trembling with fear, O Lord.

…

Seeing Your mouths, with fearful teeth, glowing like fires of cosmic dissolution, I lose my sense of direction and find no comfort. Have mercy on me! O Lord of gods, refuge of the universe.

3. Transiency. According to James, “mystical states cannot be sustained for long.” Pascal measured his experience at approximately two hours; Aquinas’s experience occurred during Mass, which indicates it could not have lasted longer than an hour or two; and Arjuna’s experience seems to have been so overwhelming that after only a short duration he pleads for it to end, saying, “O Lord! I am overwhelmed with fear. Please take again the Form I know. Be merciful. O Lord! You who are the Home of the whole universe.

4. Passivity. The experiencer feels as if he is not acting but instead being acting upon by a powerful force external to his own consciousness. This force is so tremendous that he is forced to submit his will to it. In a description of one of his mystical raptures, Augustine of Hippo, for example, begins by claiming that he was “admonished to return to myself … with [God] leading me on.”

In spite of the numerous other differences in form and content exhibited by individual mystical experiences or in mystical experiences which occur in differing cultural and religious contexts, these four marks are shared by all.

James’s Gifford Lectures on the varieties of religious experience are an insightful and delightful examination of, to use a paraphrase of his own terminology, what is most important about the human experience. Every page is filled with insight into the human condition that we all can and should take seriously and apply. I cannot recommend this book enough.